The present invention relates to a surface neuroprosthetic device for Functional Electrical Stimulation (FES) of impaired limbs, and more particularly, to a surface neuroprosthetic device having a locating system for accurate, facile, and repeatable locating of the device on to the limb, and the device electrodes on to the motor points of the muscles thereof.
FES is a means to communicate with the neuromuscular system for producing contraction in muscles or sensory input to the body. FES is used in neuroprostheses for restoring active function to paralyzed or plegic body limbs in patients suffering disease or trauma to the central nervous system, in neurological conditions such as stroke, spinal cord injury, head injury, cerebral palsy and multiple sclerosis. Surface FES systems use controlled electrical currents through electrodes placed on the surface of the body, in order to trigger contraction from muscles underlying the electrode or to input sensory stimulus. Surface neuroprostheses can coordinate the FES-activation of several muscles of the limb alone, or in coordination with voluntary activation of muscles under natural neurological control. Surface neuroprostheses are in use today for functional activities such as walking, standing, gripping/releasing objects, etc.
Electrode placement is an important issue for surface neuroprostheses. The patient or his caretaker is required to set up the neuroprosthesis each time he wishes to use it. This involves ensuring that all the electrodes are positioned accurately over the motor points of the muscles to be activated. Accurate electrode positioning ensures activation of the correct muscle without overflow to unwanted muscles, sensory tolerance of the stimulation current intensity needed to produce the desired response, and the quality of the muscle contraction. A critical factor in surface neuroprosthesis design is the provision of a means to reduce the prohibitive time and high expertise required to position the array of electrodes required to produce complex movement patterns.
Accurate electrode positioning has proved a barrier to the use of this technology and has, to date, limited the use of the surface neuroprosthesis.
In order to position an exoskeleton on to a body site (also referred to herein as “limb”) quickly, accurately and repeatedly, some means must be provided to ensure correct position and orientation of the exoskeleton relative to the body site. We refer to this means as a “locator”.
Ordinarily, devices that conform to the shape of a particular body site enable more facile positioning of the electrodes over the activation points. U.S. Pat. No. 4,432,368 to Russek describes a locator for a transcutaneous nerve stimulation (TENS) device for applying sensory FES to the lower back region, in order to provide pain relief. The electrodes are mounted on a garment which itself locates by tactile feedback on to bony landmarks: the iliac crest and the sacro-coccygeal joint. The sacro-coccygeal landmark is outside the visual field of the device user, and tactile feedback is the means used for locating the device.
U.S. Pat. No. 5,643,332 to Stein discloses a surface neuroprosthesis device for the lower limb, in which a band housing the device components is placed on to the lower leg and is located on to the tibia by a V-shaped metal plate used to position the device in a circumferential fashion. The locator angle can be bent during the initial device set-up session to fit individual patients. No longitudinal location of the V-shaped metal plate is provided for positioning the device along the longitudinal axis of the limb.
U.S. Pat. No. 5,330,516 to Nathan describes an upper limb neuroprosthesis locator. The device includes a semi-rigid exoskeleton whereby the surface electrodes are carefully positioned, by an expert, within the inside surface of the exoskeleton during an initial fitting session. Subsequently, the device user places the exoskeleton on to his arm, locating, firstly, the distal spiral portion of the device on to the bony mass of his hand, and then placing the proximal portion of the device around his forearm. The entire electrode array is constrained for accurate positioning over the limb surface, according to the electrode placement of the expert. The spiral locator allows this accurate donning of the electrode array by utilizing the underlying bone structure of the forearm and hand.
Both the leg device disclose by Stein in U.S. Pat. No. 5,643,332 and the upper limb device of Nathan (U.S. Pat. No. 5,330,516) require initial device set-up to be carried out by an expert, who positions the electrodes in the device to elicit optimal muscle contraction from the individual patient. The electrode positioning procedure requires a high degree of skill in the art in order to set up a full electrode array in an optimal manner. It would be advantageous to have a device and a method of implementing the device, which allow the surface electrode array to be manufactured in a fixed position within the device. This enables pre-arranging the surface electrode array optimally, one electrode with respect to each other, and reduces the dependence on the high degree of skill, artistry, and experience required of the clinician to carry out the initial electrode set-up procedure. The initial device set-up procedure would now be reversed with respect to the prior art: the device housing the entire electrode array is placed on the limb and adjusted to the optimal position, then locator system is positioned and attached to the device, such that the device can be repeatably located to this optimal position by the patient. This would require the provision of fast accurate means for positioning the device longitudinally as well as circumferentially on to a conical upper or lower limb segment.
It is thus manifest that fast and accurate electrode positioning has proved to be a problematic issue of central importance to the implementation of surface neuroprostheses. Moreover, neurological deficits such as perceptual or motor deficiencies may affect the requirements of the locator system.
Perceptual difficulties in neurological conditions such as stroke can often present a challenge to recognition of device orientation in space relative to the limb. Here the problem is to provide a means for making the device orientation and any rotation-maneuver required for donning the device on a limb “obvious”, fast and easy.
In addition, motor deficiency can take the form of limb weakness, paralysis or spasticity, which make donning the device a challenge. In hemiplegia resulting from stroke or brain injury, the side of the body on which the neuroprosthesis is donned is often plegic. The donning action must often be carried out using solely the contra-lateral non-plegic hand. The posture of plegic limb is often problematic where spasticity results in reduced voluntary movements and also limited passive mobility of the limb. The limb can be set at the extreme of its range of motion, for example, full adduction at the shoulder joint resulting in the upper arm being held tightly against the trunk. This abnormal limb posture and lack of limb mobility can present biomechanical problems in donning the device and locating it on to the limb.
It is further noted that the limitations and deficiencies of known surface neuroprostheses devices are particularly glaring regarding upper-arm surface neuroprosthesis applications. To the best of our knowledge, no upper-arm surface neuroprosthesis device has been successfully developed heretofore.
There is therefore a recognized need for, and it would be highly advantageous to have, a neuroprosthetic device and method for functional electrical stimulation of impaired limbs having a reliable locating system that provides for accurate, facile, simple, fast and repeatable positioning and orientation of the device over the activation points of the muscles, such that the FES is effective and comfortable.